Embodiments of the inventive concepts relate to a perpendicular magnetic layer and a perpendicular magnetic layer structure, which have a ferromagnetic property. In addition, embodiments of the inventive concepts relate to a magnetoresistive element and a perpendicular magnetic recording medium, which use the perpendicular magnetic layer structure.
A perpendicular magnetic layer magnetized in a direction perpendicular to a surface of the layer attracts attention as an information recording layer with the development of high-density and large-capacity magnetic storage or memory devices such as a magnetic disk device (a hard disk) or a non-volatile magnetic random access memory (MRAM) device. A perpendicular magnetic material having a high magnetic anisotropy energy density (Ku) is needed to improve a recording density by miniaturizing the recording medium of the hard disk or a tunnel magnetoresistive element (e.g., a magnetic tunnel junction (MTJ) element) of the MRAM device, which uses the perpendicular magnetic layer. The MTJ element makes a recording bit of the MRAM device. In particular, in the MTJ element, a low saturation magnetization and a characteristic capable of easily forming a flat layer are needed together with the high Ku. The low saturation magnetization is need to reduce a characteristic change of the MTJ element by a leakage magnetic field of the perpendicular magnetic layer or to reduce the influence of the leakage magnetic field on neighboring elements. The flat layer is needed to form the MTJ element having a multi-layered structure without a height difference. In addition, when the perpendicular magnetic layer is used as the information recording layer of the MTJ element for the MRAM device, it is required to reduce power consumption of an information recording operation using a current flowing through the MTJ element (i.e., a spin-transfer-torque (STT) recording operation). To achieve this, the perpendicular magnetic layer needs to have a low magnetic damping constant. Naturally, the perpendicular magnetic layer needs to have a ferromagnetic transition temperature (Curie temperature) much higher than a room temperature.
For example, a cobalt-based alloy material such as a cobalt-platinum-chromium (Co—Pt—Cr) alloy has been known as the perpendicular magnetic layer of a perpendicular magnetic recording medium. In addition, a Lb 10-type iron-platinum (FePt) alloy having a very high magnetic anisotropy energy density (Ku) is used in patent document 1. An atomic alternating laminated layer of Co and Pt is used as the perpendicular magnetic layer of the MTJ element in non-patent document 1. This is a structure obtained by applying a high magnetic anisotropy energy density (Ku) of a CoPt alloy.
However, since the known perpendicular magnetic materials include noble metals, they are expensive and generally have great magnetic damping. Meanwhile, a manganese-gallium alloy having small magnetic damping and not using a noble metal is considered as a candidate material of the perpendicular magnetic layer (non-patent document 2). However, since it is difficult to form the manganese-gallium alloy material into a flat layer, it is difficult to improve the quality of a magnetic recording medium or MTJ element using this material.
In non-patent document 3, a homogeneous manganese-gallium-nitrogen (MnGaN) layer having a cubic system (E21-type) structure may be obtained by introducing nitrogen into a MnGa alloy layer, a perpendicular magnetic layer may be formed using this layer, and a very flat layer may be obtained at a high formation temperature of about 500 degrees Celsius. However, a magnetic anisotropy energy density (Ku) of this layer is as small as a fraction of a magnetic anisotropy energy density (Ku) of a D022-type MnGa alloy not including nitrogen.                [Patent document 1] WO 2014/004398 A1        [Non-patent document 1] “Ultralow-Voltage Spin-Transfer Switching in Perpendicularly Magnetized Magnetic Tunnel Junctions with Synthetic Antiferromagnetic Reference Layer”, Appl. Phys. Express, Vol. 6, No. 11, p113006 (2013), K. Yakushiji, A. Fukushima, H. Kubota, M. Konoto, and S. Yuasa.        [Non-patent document 2] “Long-Lived Ultrafast Spin Precession in Manganese Alloys Films with a Large Perpendicularly Magnetic Anisotropy”, Phys. Rev. Lett., Vol. 106, No. 11, p117201 (2011), S. Mizukami, F. Wu, A. Sakuma, J. Walowski, D. Watanabe, T. Kubota, X. zhang, H. Naganuma, M. Oogane, Y. Ando, and T. Miyazaki.        [Non-patent document 3] “Ferromagnetic MnGaN thin films with perpendicular magnetic anisotropy for spintronics applications”, Appl. Phys. Lett, Vol. 107, No. 3, p. 032403 (2015), H. Lee, H. Sukegawa, J. Liu, T. Ohkubo, S. Kasai, S. Mitani, and K. Hono.        [Non-patent document 4] “Magnetic Studies of the Metallic Perovskite-Type Compounds of Manganese”, J. Phys. Soc. Jpn., Vol. 44, No. 3, pp. 781-791 (1978), D. Fruchart and E. F. Bertaut.        